US7046745B2 - Signal processing circuit - Google Patents
Signal processing circuit Download PDFInfo
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- US7046745B2 US7046745B2 US09/986,925 US98692501A US7046745B2 US 7046745 B2 US7046745 B2 US 7046745B2 US 98692501 A US98692501 A US 98692501A US 7046745 B2 US7046745 B2 US 7046745B2
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
- G11B20/10—Digital recording or reproducing
- G11B20/10009—Improvement or modification of read or write signals
- G11B20/10046—Improvement or modification of read or write signals filtering or equalising, e.g. setting the tap weights of an FIR filter
- G11B20/10055—Improvement or modification of read or write signals filtering or equalising, e.g. setting the tap weights of an FIR filter using partial response filtering when writing the signal to the medium or reading it therefrom
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B20/00—Signal processing not specific to the method of recording or reproducing; Circuits therefor
- G11B20/10—Digital recording or reproducing
- G11B20/10009—Improvement or modification of read or write signals
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/02—Recording, reproducing, or erasing methods; Read, write or erase circuits therefor
- G11B5/09—Digital recording
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/004—Arrangements for detecting or preventing errors in the information received by using forward error control
- H04L1/0045—Arrangements at the receiver end
- H04L1/0054—Maximum-likelihood or sequential decoding, e.g. Viterbi, Fano, ZJ algorithms
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/012—Recording on, or reproducing or erasing from, magnetic disks
Definitions
- the present invention is generally related to a signal processing system for either a magnetic disk apparatus or an optical disk apparatus. More specifically, the present invention is directed to a high-efficiency demodulating method of a high-order partial response system such as an EEPRML (Extended Extended Partial Response Maximum Likelihood) signal processing system and an EEEPRML (Extended EEPRML) signal processing system.
- a high-efficiency demodulating method of a high-order partial response system such as an EEPRML (Extended Extended Partial Response Maximum Likelihood) signal processing system and an EEEPRML (Extended EEPRML) signal processing system.
- the partial response maximum likelihood (will be abbreviated as a “PRML” hereinafter) signal processing system combining the partial response class 4 (PR4) and the maximum-likelihood decoding system are practically available as a high-efficiency signal processing system.
- a high-efficiency signal processing system implies a system capable of realizing a desirable data error rate at a low SIN (signal-to-noise) ratio.
- SIN signal-to-noise
- FIG. 1 shows a structural example of the construction of a general magnetic disk apparatus using a PRML signal processing system.
- Original data is supplied to an error correcting encoder 7 through an interface circuit 8 so that the original data is added with redundant data necessary for error correction.
- the original data added with redundant data is subjected by a data modulator 6 to modulation necessary for the PRML system and is recorded on a magnetic disk 3 by a magnetic head 4 through a recording/reproducing amplifier 5 .
- a signal reproduced from the magnetic disk 3 is passed through the recording/reproducing amplifier 5 and then PRML-processed by a data demodulator 1 .
- the demodulated data is error-corrected by an error correcting decoder 2 and is thereafter converted through the interface circuit 8 into the original data.
- This data modulator 6 and data demodulator 1 will now be explained in more detail with reference to FIG. 2 indicating a relationship between a magnetic recording/reproducing system and a partial response system.
- a first description will now be made of process operations executed on the data recording side.
- the data outputted from the error correcting encoder 7 is penetrated through a precoder 9 constructed of a delay element and modulo (Mod. 2), and then is recorded via a recording amplifier 5 on a recording medium.
- This precoder 9 is employed so as to prevent erroneous propagation of data which is caused during the demodulating operation.
- the magnetization on the recording medium is reproduced as a waveform having a differential characteristic by the recording/reproducing head.
- PR4 may regard this differential characteristic as a differential system of (1 ⁇ D).
- symbol AD@ implies a 1-bit delay calculator.
- the reproduced waveform is supplied to the equalizer 10 so as to be equalized in such a manner that a response of the waveform becomes (1+D).
- a total transfer characteristic in the output of the equalizer becomes (1 ⁇ D 2 ).
- a data discrimination of the data is carried out in the maximum decoder 11 .
- PR4 implies that the isolated waveform is regarded as a waveform enlarged to 2 time slots, as indicated in FIG. 3A . This waveform owns such a characteristic having (1+D). Also, as indicated in FIG. 3B , EPR4 implies that the isolated waveform is regarded as a waveform enlarged to 3 time slots. This waveform owns such a characteristic having (1+D) 2 . Furthermore, as indicated in FIG. 3C , EEPR4 implies that the isolated waveform is regarded as a waveform enlarged to 4 time slots. This waveform owns such a characteristic having (1+D) 3 .
- a total transfer characteristic of EEPR4 constitutes (1 ⁇ D) ⁇ (l+D) 3 as a product of a transfer characteristic of an isolated waveform and another transfer characteristic of a magnetic recording system.
- An impulse response of the EEPR4 system determined by this product is represented in FIG. 4 .
- an isolated waveform of EEPR4 owns amplitude characteristics (normalized ratio) of 1, 3, 3, 1 every bit period.
- a response of an isolated pulse is obtained by superimposing the isolated waveforms inverted along the upper/lower directions with each other by shifting a 1-bit time period.
- FIG. 5 there is shown a trellis diagram of EEPRML obtained by combining a maximum likelihood decoder with EEPR4.
- symbol “ak” indicates an input signal to EEPRML at a time instant “k”.
- reference numeral 12 indicates a state
- reference numeral 13 shows a state transition.
- An upper stage of a label (ak/yk) and a lower stage thereof indicate an input signal value and an output signal value, respectively.
- the states of the respective signal processing systems are determined by the past input signal series.
- EEPRML a level of a reproduction signal at the present time instant is influenced by signals over the past 4 time slots. Assuming now that a state at a time instant “k” is equal to “sk”, it is given as
- sk ((ak ⁇ 4, ak ⁇ 3, ak ⁇ 2, ak ⁇ 1)1ak(1,0)), and a total number of states becomes 16.
- state transitions originated from a plurality of states are collected to a specific state at the time instant “k”.
- a branch metric a squared value of a difference between an output signal and an input signal, which are indicated at a low stage of each label.
- branch metric an accumulated value of branch metrics until the present time instant with respect to each of the states.
- the performance of EEPRML is determined by a minimum free distance (Dfree).
- Dfree implies a minimum difference of path metrics among various sorts of combinations from a specific node to another specific node on the trellis diagram shown in FIG. 5 . It is known that “Dfree” of EEPRML is equal to 6. Furthermore, distances between signals subsequent to “Dfree” become 8 and 10. These distances between signals of EEPRML are determined by a data pattern entered into the maximum likelihood decoder. In particular, a distance between-signals is defined by a continuous time at which a pattern is changed from 0 to 1, or from 1 to 0.
- the conventional MTR code is described in, for example, “Maximum Transition Run Codes for Data Storage Systems”, IEEE Transactions on Magnetics, volume 32, No. 5, September 1996, pages 3992 to 3994.
- the above-described MTR code owns a function to restrict that inverting of a pattern occurs more than 3 times.
- a limitation can be made to the pattern inversion for more than 10 distances between signals of EEPRML.
- an S/N ratio of a signal can be equivalently improved.
- the code rate becomes 4/5 and the like. This code rate value is low, as compared with the normally used 16/17 GCR (Group Coded Recording) and 8/9 GCR.
- a code rate loss becomes large, and a total coding gain cannot be always satisfied.
- a gain becomes approximately 2.2 dB, since the distance between signals is improved-from 6 to 10.
- An object of the present invention is to provide a generally-used method for expanding the distance between signals of a high order partial response system, especially, the EEPRML system and the EEEPRML system irrespective of a code under use.
- an object of the present invention is to provide a method for equivalently expanding a distance between signals without newly producing a code rate loss, since the 16/17 GCR, or the 8/9 GCR used in the PRML signal process operation for a magnetic disk apparatus can be directly applied.
- a response of an isolated pulse waveform is changed from the original response of EEPRML, or EEEPRML, so that the distance between signals can be expanded.
- a response of an isolated pulse is selected to be an symmetrical waveform. For instance, as previously described, in the EEPRML system, the response of the isolated pulse waveform becomes 1, 2, 0, ⁇ 2, ⁇ 1.
- a code is equal to a binary number of ⁇ 1, 0 ⁇ .
- a value of 1 corresponds to such an error case that 1 erroneously becomes 0;
- a value of ⁇ 1 corresponds to such an error case that 0 erroneously becomes 1;
- a value of 0 corresponds to such an error case that no error occurs.
- the error patterns of the EEPRML system are classified in accordance with this definition:
- An actual code error pattern of (A) is such a case that (a, b, 1, 0, 1, c, d) erroneously becomes (a, b 0, 1, 0, c, d), or vice versa.
- An actual code error pattern of (B) 1) is such a case that (1, 0, 1, a, b, 1, 0, 1) erroneously becomes (0, 1, 0, a, b, 0, 1, 0), or vice versa.
- An actual code error pattern of (B) 2) is such a case that (1, 0, 1, 0, 1, 0, 1) erroneously becomes (0, 1, 0, 11 0, 1), or vice versa.
- symbols “a”, “b”, “c”, and “d” are arbitrary.
- Two sorts of data streams “ ” and “ ”, shown in FIG. 6 own such values of “010abcde”. That is, only 3 bits thereof are different form each other.
- FIG. 7 indicates waveforms corresponding to these data streams.
- a distance between signals of the two sorts of patterns is 6.
- FIG. 8 represents a waveform corresponding to the above-described (B) 1).
- EEPRML has a transfer characteristic of (1 ⁇ D) ⁇ (1+D)3.
- isolated waveforms having responses 1, 3, 3, 1 are alternately repeated in such a manner of positive-negative-positive.
- a total signal energy 3 isolated waveforms i.e., 60 is reduced to 12.
- the essential aspect in order to enlarge the distance between signals is to establish a measure how to concentrate energy without losing the energy (electric power) of the isolated waveform.
- a means for concentrating energy of a signal an isolated waveform is filtered by an all-pass filter 14 to satisfy a minimum, phase transition condition, which could be cleared based on the communication theory.
- a minimum phase transition condition implies that a zero point and a pole of a transfer function of a signal given by a rational function are present within the same unit circumference.
- L(t) is a symmetrical waveform with respect to right/left directions.
- a ratio (TW/T) of a half bandwidth to a time width T of a pulse to be recorded is defined as a normalized line density.
- TW/T a ratio of a half bandwidth to a time width T of a pulse to be recorded
- the waveform may be recorded in the high density.
- a Lorentz waveform whose normalized line density is selected to be approximately 2.5 is used.
- the energy is concentrated to the front half portion of the isolated waveform.
- a clock signal timing signal
- a jitter component temporary fluctuation
- the clock signal (timing signal) extracting circuit becomes complex. This practical reason makes it difficult.
- the above-described asymmetric characteristic is given to the waveform by such a manner that the timing extraction is carried out under condition of a front term in a right hand, and thereafter an asymmetrical response given by a rear term in the right hand is given by the discrete time filter. At this time, a selection is made of such asymmetrical coefficients C 0 , C 1 , . . . , C n that the S/N ratio given by the formula (1) becomes maximum.
- a table 1 represents a typical characteristic of such a partial response that a state number thereof is 16.
- a distance of an isolated pulse indicated in this table 1 is directly equal to electric power owned by the isolated pulse itself.
- a minimum distance corresponds to such minimum distance among distances on a trellis diagram of partial response signal having given coefficients.
- a distance of the minimum distance/isolated pulse may constitute an index for there is a particular improvement in the characteristic.
- the characteristics of the table 1 and the table 2 correspond to such a case that the normalized line density is 2.5.
- the S/N ratio can be improved, but also the length of the code error can be improved, as compared with the long continued errors caused by the conventional EEPRML and EEEPRML systems. That is, giving the utilization efficiency of the energy of the partial response for giving this distance.
- the partial response system having the coefficient according to the present invention may have the advantages as to this point, as compared with that of the normal EEPRML. As a result, it can be seen that the S/N can be effectively improved with respect to the EEPRML having the symmetrical coefficient.
- a table 2 represents a typical characteristic of such a partial response that a state number thereof is 32.
- the major error bit length is the 1-bit error bit length, or the 3-bit error bit length.
- the present invention has such a feature that the error correction can be effectively performed by combining with the error correction code having the code error correcting capability with respect to at least the 1-bit continuous error, and the 3-bit continuous error.
- FIG. 1 is a structural diagram for indicating the conventional data demodulating circuit
- FIG. 2 is a schematic diagram for showing the relationship between the PRML demodulating system and the magnetic recording/reproducing system
- FIG. 3A , FIG. 3B , and FIG. 3C are graphic representations for showing the conventional isolated waveform response of the partial response
- FIG. 4 is a graphic representation for indicating the conventional isolated waveform of EEPR4 and the conventional isolated pulse response
- FIG. 6 shows such a diagram that the conventional pattern giving the distance between signals “6” of EEPRML is indicated on the trellis diagram
- FIG. 7 indicates an example of waveforms giving a distance between signals 6 of EEPRML
- FIG. 8 indicates an example of waveforms giving a distance between signals 8 of EEPRML
- FIG. 9A and FIG. 9B are diagrams for indicating the reason why the conventional distance between signals of EEPRML is reduced to 6;
- FIG. 10 schematically represents a basic idea for concentrating energy of isolated waveform responses of a partial response according to an embodiment of the present invention
- FIG. 11 is a graphic representation for representing an example of a minimum phase transition waveform according to an embodiment of the present invention.
- FIG. 12 is a schematic block diagram for showing a circuit arrangement according to an embodiment of the present invention.
- FIG. 13A and FIG. 13B are schematic block diagrams for indicating a circuit arrangement of a discrete time filter according to an embodiment of the present invention.
- FIG. 14 is a trellis diagram having coefficients of the embodiment of the present invention.
- FIG. 15 schematically represents a 16-state maximum likelihood decoder as an example of the embodiment of the present invention.
- FIG. 12 there is shown a structural example of an actual circuit arrangement according to the present invention.
- an output of a magnetic head is supplied via a preamplifier to an AGC (automatic gain control circuit) and LPF (low-pass filter) 15 .
- AGC automatic gain control circuit
- LPF low-pass filter
- This magnetic head output is controlled by the AGC/LPF 15 in such a manner that an amplitude of a signal becomes a constant, noise components other than a desirable frequency range are removed by this AGC/LPF 15 .
- This LPF output signal is discrete-quantized by an ADC 16 , and then the discrete-quantized signal is inputted into an equalizer 10 .
- the reproduction signal derived from the magnetic head is equalized in such a manner that this reproduction signal has a partial response characteristic of (1 ⁇ D 2 ).
- a clock signal required to operate the ADC 16 is produced from the output signal of this equalizer 10 by a PLL circuit 20 .
- a control signal of the AGC/LPF 15 is also obtained from an AGC control circuit 21 .
- an output signal of the equalizer 10 is applied to a discrete time filter 18 so as to produce such a filter output signal having a response characteristic of (1 ⁇ D 2 ) (C 0 +C 1 D+ . . . +C n D n ).
- this filter output signal is supplied to a maximum likelihood decoder 19 so as to discriminate data.
- This discriminate data is demodulated by a 16/17 (or 8/9) ENDEC 23 to obtain original user data from an output of this 16/17 ENDEC 23 . It should be understood that since the output signal of the equalizer 10 is supplied to a maximum likelihood decoder 22 of PR4, the normal PRML demodulation data is obtained. Next, an arrangement of the discrete time filter is indicated.
- the output of the equalizer 10 is added to an input terminal 30 of the discrete time filter.
- An output obtained by processing this signal by a 3-time coefficient multiplier 31 , another output obtained by delaying this signal by 1 bit in a delay circuit 36 to process the 1-bit delayed signal by a 2-time coefficient multiplier 32 , and another output obtained by delaying this signal by 2 bits to process the 2-bit delayed signal by a 1-time coefficient multiplier 33 are added by an adder 34 , so that a desirable filter coefficient is obtained at an output terminal 35 .
- a pulse response is given as 3, 2, ⁇ 2, ⁇ 2, ⁇ 1 based on a formula (3).
- a discrete time filter may be similarly constructed by employing coefficients represented in a table 1.
- the output of the equalizer 10 is added to an input terminal 60 of the discrete time filter.
- An output obtained by processing this signal by a 2-time coefficient multiplier 51 , another output obtained by delaying this signal by 1 bit in a delay circuit 56 to process the 1-bit delayed signal by a 5-time coefficient multiplier 52 , another output obtained by delaying this signal by 2-bits to process the 2-bit delayed signal by a 3-time coefficient multiplier 53 , and another output obtained by delaying this signal by 3 bits to process the 3-bit delayed signal by a 2-time coefficient multiplier 54 are added by an adder 55 , so that a desirable filter coefficient is obtained at an output terminal 56 .
- a pulse response is given as 2, 5, 1, ⁇ 3, ⁇ 3, ⁇ 2 based on a formula (3).
- a discrete time filter may be similarly constructed by employing coefficients represented in a table 2.
- FIG. 15 schematically represents one embodiment mode of the 16-state maximum likelihood decoder Of FIG. 14 .
- This processing circuit is arranged by a branch metric generating unit 40 , an ACS circuit 41 , and a path memory 42 .
- the ACS circuit 41 executes an adding process, a comparing process, and a selecting process between the path metric values and the branch metric values of the 16 states, so that a path metric value with respect to a most likelihood path is generated.
- the path memory 42 produces decoded data based upon the comparison results of the respective states. It should be noted that the path metric is initialized by an initial setting circuit 43 when this circuit is initiated.
- the controller 102 Upon receipt of a data recording instruction, the controller 102 issues an instruction to a servo control circuit 103 such that a recording/reproducing head 4 is moved to a position to be recorded (namely, track). After the transport of the recording/reproducing head is accomplished, recording data is supplied via a recording data processing circuit 104 , an R/W amplifier 5 , and a recording/reproducing head 4 to a recording medium 3 so as to be recorded on this recording medium 3 .
- the controller 102 Upon receipt of a data reproducing instruction, the controller 102 issues an instruction to the servo control circuit 103 such that the recording/reproducing head 4 is moved to a position on which data has been recorded (namely, track). After the movement of the recording/reproducing head 4 has been completed, a signal recorded on the recording medium 3 is inputted via the recording/reproducing head 4 and the R/W amplifier 5 to the data demodulating circuit 1 . The demodulation data demodulated by the data modulating circuit 1 is outputted to the controller 102 . After the controller 102 confirms correctness of the demodulation data, the controller 102 transfer the demodulation data to the external apparatus.
- the data demodulating system is arranged by the AGC circuit for making the amplitude of the head reproduction waveform constant/the band-eliminating filter (LPF) 15 for eliminating the noise outside the signal band; the ADC 16 for sampling the reproduction signal; the equalizer 10 for eliminating the interference among the codes of the reproduction waveform; the PLL 20 for determining the sampling timing of the ADC 16 ; the data demodulating circuit 1 functioning as a major circuit of the present invention and the decoder 23 - 2 for performing the decoding process (8/9 GCR decoder) of the demodulation data.
- the microcomputer 101 executes the process operations of the overall apparatus such as the controller 102 and the data demodulating circuit 1 .
- the microcomputer 101 executes the following process operations. That is, a detection of a detection result of an irregular code detecting circuit 128 , and a setting operation is made of a register 130 for applying information to a multiplexer 129 for switching a PRML processing unit 22 and an MEEPRML processing unit 19 . Furthermore, the data demodulating system may be alternatively arranged by adoptively switching these circuits in response to the recording density by employing another MEEPRML circuit having the coefficient listed in the table 1. This alternative arrangement may be realized by setting a desirable coefficient of the discrete time filter 18 to the register 131 by way of the microcomputer 101 .
- the error correction suitable for this error length is carried out. Thereafter, the decoding process operation such as 8/9 GCR is performed by the decoder 23 . This error correction and the decoding process operation are preferable so as to prevent the error codes from being enlarged.
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Abstract
Description
S/N=distance between signals/noise power×noise correlative coefficient) (1).
-
- 1) (1, −1, 1, 0, 0, 1, −1, 1)
- 2) (1, −1, 1, −1, 1).
-
- (C) is a 1-bit isolated pulse error.
L(t)=1.O/(l+(2t/TW)2 (2)
where symbol “TW” gives a half bandwidth.
PR(D)=(1−D 2)×(C 0 +C 1 D+ . . . +C n D n) (3)
SK=a k−5, a k−4, a k−3, a k−2, a k−1
Y k =C0a k+C 1 a k−1+(C 2 −C 0)a k−2+(C 3 −C 1) a k−3−C2a k−4−C3a k−5 (4)
Claims (14)
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US09/986,925 US7046745B2 (en) | 1997-08-04 | 2001-11-13 | Signal processing circuit |
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JP20882097A JP3533315B2 (en) | 1997-08-04 | 1997-08-04 | Signal processing circuit |
US09/124,840 US6337889B1 (en) | 1997-08-04 | 1998-07-30 | Partial response demodulating method and apparatus using the same |
US09/986,925 US7046745B2 (en) | 1997-08-04 | 2001-11-13 | Signal processing circuit |
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US5291499A (en) * | 1992-03-16 | 1994-03-01 | Cirrus Logic, Inc. | Method and apparatus for reduced-complexity viterbi-type sequence detectors |
JPH07302467A (en) | 1994-05-02 | 1995-11-14 | Hitachi Ltd | Waveform equalizing channel |
US5585975A (en) * | 1994-11-17 | 1996-12-17 | Cirrus Logic, Inc. | Equalization for sample value estimation and sequence detection in a sampled amplitude read channel |
JPH097313A (en) | 1995-06-22 | 1997-01-10 | Matsushita Electric Ind Co Ltd | Digital information reproducer |
US5619539A (en) * | 1994-02-28 | 1997-04-08 | International Business Machines Corporation | Data detection methods and apparatus for a direct access storage device |
US5784415A (en) * | 1993-06-14 | 1998-07-21 | International Business Machines Corporation | Adaptive noise-predictive partial-response equalization for channels with spectral nulls |
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DE3914243A1 (en) * | 1989-04-29 | 1990-10-31 | Bruker Analytische Messtechnik | MAGNETIC SYSTEM WITH SUPERCONDUCTIVE FIELD PULES |
US5568051A (en) * | 1992-05-12 | 1996-10-22 | Kabushiki Kaisha Toshiba | Magnetic resonance imaging apparatus having superimposed gradient coil |
US5592087A (en) * | 1995-01-27 | 1997-01-07 | Picker International, Inc. | Low eddy current radio frequency shield for magnetic resonance imaging |
US6369464B1 (en) * | 1999-07-02 | 2002-04-09 | Bruker Ag | Active shielded superconducting assembly with compensation of magnetic field disturbances |
US6556012B2 (en) * | 2000-01-21 | 2003-04-29 | Kabushiki Kaisha Toshiba | Magnetic resonance imaging apparatus |
DE10354676B4 (en) * | 2003-11-22 | 2006-12-21 | Bruker Biospin Gmbh | Magnetic system with planar, multilayer arrangement of superconducting wires |
DE10354677B4 (en) * | 2003-11-22 | 2006-09-21 | Bruker Biospin Gmbh | Additional stray field shielding of a superconducting magnet coil system |
DE102004023073B3 (en) * | 2004-05-11 | 2006-01-05 | Bruker Biospin Gmbh | Magnetic system with shielded regenerator housing and method for operating such a magnet system |
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1998
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- 2001-11-13 US US09/986,925 patent/US7046745B2/en not_active Expired - Fee Related
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Also Published As
Publication number | Publication date |
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JP3533315B2 (en) | 2004-05-31 |
JPH11168514A (en) | 1999-06-22 |
US6337889B1 (en) | 2002-01-08 |
US20020064242A1 (en) | 2002-05-30 |
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